Scanning electron microscope and method for dimension measuring by using the same

ABSTRACT

An electron beam which can transmit through part of a specimen and can reach a portion not exposing to the electron beam is irradiated and a scanning image is obtained on the basis of a signal secondarily generated from a portion irradiated with the electron beam. Dimension-measuring start and end points are set on the scanning image and a dimension therebetween is measured. A cubic model is assumed, the cubic model is modified so as to match the scanning image, and dimension measurement is carried out on the basis of a modified cubic model.

BACKGROUND OF THE INVENTION

This is a continuation application of Ser. No. 08/979,327, filed Nov.26, 1997 now U.S. Pat. No. 5,969,357; which is a continuationapplication of Ser. No. 08/970,201, filed Nov. 14, 1997, now U.S. Pat.No. 5,866,904; which is a continuation application of Ser. No.08/827,444, filed Mar. 28, 1997, now abandoned; which is a continuationapplication of Ser. No. 08/706,779, filed Sep. 3, 1996, now abandoned;which is a continuation application of Ser. No. 08/386,766, filed Feb.10, 1995, now U.S. Pat. No. 5,594,245; which is a continuation-in-partapplication of Ser. No. 08/160,336, filed Dec. 2, 1993, now U.S. Pat.No. 5,412,210; which is a continuation-in-part application of Ser. No.08/039,705, filed Mar. 29, 1993, now abandoned; which is acontinuation-in-part application of Ser. No. 07/773,729, filed Oct. 9,1991, now abandoned.

The present invention relates to an apparatus and a method of observingsurface configurations by using an electron beam, and especiallyprovides an apparatus and a method by which observation of eitherconfigurations of the bottom of a deep hole or residues therein, usedfrequently in semiconductor processes, can be permitted.

The scanning electron microscope, in which an electron beam is scannedon a specimen and secondary electrons generated from the specimen aredetected, has been utilized widely in the fields of biology andengineering. Especially, in the semiconductor industry, high-integrationformation has advanced and as a result, inspection based or opticalmicroscopes has become impossible, and the utilization of the scanningelectron microscope has been promoted. In a scanning electron microscopeused for semiconductors, it is conventional to use an electron beam oflow energy of 1 keV or less in order to avoid charging on insulators.

In the semiconductor industry, the scanning electron microscope isutilized for not only inspect on of appearance of completedsemiconductors but also inspection in mid-course of the manufacturingprocess. For example, it is used for inspection of appearance,inspection of dimension and inspection of through-holes in mid-course ofthe process.

As a result of the advancement of high-integration formation ofsemiconductor devices, it has become impossible for the method using theconventional scanning electron microscope to inspect openings ofthrough-holes.

Referring to FIG. 2, problems encountered in observing a deep hole withthe conventional scanning electron microscope will be described. FIG. 2shows a case where a primary electron beam 1 of low energy irradiates aflat portion and a hole 3 of a specimen. Thanks to the absence of anyobstacles, almost all of the number of secondary electrons 2 generatedat the flat portion can be detected. Similarly, reflection electronsconcurrently discharged can also be detected. In the case of irradiationof the hole 3, however, generated secondary electrons 2 impinge on theside wall of the hole 3 and consequently cannot escape from the hole 3to the outside. The energy of reflection electrons is higher than thatof secondary electrons but is not so high that the reflection electronscan penetrate through the side wall, and the reflection electrons arethus blocked by the side wall.

The present invention is further concerned with a method for displayinga scanning image of a specimen and an apparatus therefor. Examples ofsuch specimens are devices and parts as represented by a semiconductordevice, a photomask substrate inclusive of a multi-layer structure masksuch as a phase shift mask, a display device such as a liquid crystaldevice or a CCD, a wiring board, a memory medium such as an opticaldisc, metal or polymer materials, cellular issues and other livingbodies.

Additionally, both intermediate produces and finished goods areconsidered specimens for the purposes of the invention. The presentinvention handles these objects and is effective for use in observation,inspection, measurement and analysis of them or in monitoring techniqueduring treatment of specimens.

By way of example, in the field of observation of a fine structure of aspecimen, of a scanning microscope using an electron beam having anenergy level of several hundreds of eV to several tens of keV, and atransmission-type electron microscope using an electron beam of severaltens of keV to several MeV, have been used for imaging a specimen anddisplaying the image on a specimen image display apparatus. Specimenimage display techniques using the above electron microscope techniquesare described in the literature; see, for example, "Fundamentals andApplications of Scanning Electron Microscope", originally edited andtwice published by Kyohritsu Shuppan Kabushiki-Kaisha, May 25, 1985.

Disadvantageously, however, the conventional techniques described abovehave encountered difficulties in performing high-resolution ornon-destructive observation of a surface structure having largeunevenness or precipitous unevenness, and of an internal structure of aspecimen.

SUMMARY OF THE INVENTION

FIG. 3 shows results of calculating the relationship between the aspectratio (depth/opening diameter) of a hole and the ratio of signalsescaping from the hole. A signal at the surface (aspect ratio=0)corresponds to 1. This calculation demonstrates that observation ofholes of an aspect ratio exceeding 2 is impossible with the conventionalscanning electron microscope.

In the present invention, in order to solve the aforementioned problems,a primary electron beam is used which has such high energy as to allowreflection electrons generated at the bottom of a hole to penetratethrough the side wall of the hole.

Referring to FIG. 1, the principle of observation of deep holes by usinga primary electron beam of high energy will be described.

A case where a primary electron beam 4 of high energy irradiates asurface portion resembles a case where the surface portion is irradiatedwith low energy. However, in the case of irradiation on the interior ofa hole, the circumstances differ greatly. Secondary electrons 2 areabsorbed by the side wall but reflection electrons 6 penetrate throughthe side wall to escape from the surface. When the reflection electrons6 pass through the surface, they generate secondary electrons 5. Sincethe secondary electrons 5 and reflection electrons 6 have moreinformation about the bottom of the hole 3, an image of the interior ofthe hole can be obtained by detecting these electrons.

Thus, one of the aspects of the present invention resides in that theprimary electron beam has sufficiently high energy to allow reflectionelectrons to penetrate through the side wall, thereby permittingobservation of the bottom of high-aspect-ratio holes, which observationhas hitherto been impossible. The primary electron beam penetrates aninsulating layer (≦2 μm thickness) of a semiconductor device when it hasenergy sufficient for the reflection electrons to penetrate through theside wall. This results in allowing electrons in the insulating layer tomove, i.e. the layer becomes conductive so that the layer is not subjectto charging. Further, when the primary electron beam has an energy levelas defined by the present invention, the beam itself does not cause theinsulating layer of the semiconductor device to become charged.

Another object of the invention is to provide a scanned specimen imagedisplaying technique capable of performing non-destructive observationof an internal structure of a specimen, and of a specific structure of adefect, foreign material or the like.

Still another object of the invention is to provide a scanned specimenimage displaying technique capable of performing high-resolutionobservation of a surface structure having large unevenness orprecipitous unevenness, and an internal structure of a specimen.

Still another object of the invention is to provide a scanned specimenimage displaying technique capable of obtaining three-dimensionalinformation and tomographic information about surface and internalstructures of a specimen.

Still another object of the invention is to provide a scanned specimenimage displaying technique capable of performing high-resolutionobservation of an electrically non-conductive specimen.

Still another object of the invention is to provide a specimen whosesurface and internal structures can be observed more effectively underthe irradiation of a high-energy particle beam.

The above and other objects and novel features of the invention willbecome apparent from the description contained in the presentspecification and from the accompanying drawings.

Typical forms of the invention to be disclosed in the presentapplication will be outlined briefly as below.

More particularly, in the present invention, a scanning particle beam isirradiated to a specimen to act on the specimen so as to produce primaryinformation such as back-scattered particles, X-rays and photons, andthe primary information also interacts with the specimen to producesecondary information, such as secondary electrons and photons, which isused as a main signal for formation of an image.

In a particular embodiment, an electron beam having an energy level of50 keV or more is used as the scanning particle beam, and secondaryelectrons or electromagnetic waves resulting from interaction ofreflection electrons, generated under the irradiation of the electronbeam, with the specimen are detected as the secondary information toconstruct a scanned specimen image.

In another embodiment, at least one of tomographic and three-dimensionalimages is formed on the basis of a plurality of specimen images observedwith two or more particle beams which are different from each other inat least one of incident energy and angle.

When a part standing for a target or object to be observed, that is, atest part, is inside a specimen, a scanning particle beam must have anenergy which satisfies the following requirements: the scanning particlebeam must be able to transmit or penetrate through the specimen to reachthe test part, and the scanning particle beam must interact with thetest part to generate primary information such as back-scatteredparticles. The primary information itself must have sufficient energy toalso interact with the specimen so as to generate secondary informationsuch as secondary electrons.

The energy required for the scanning particle beam, that is, the primarybeam, is determined by taking into consideration the degree of backscattering and forward scattering of a part of the specimen present on apath of the beam (i.e., a part overlying the test part) The degree ofscattering depends on well known parameters (density, thickness and thelike of that part).

In back scattering, it is preferable that the test part have a largecontrast to its surroundings, and especially to the beam passage partoverlying the test part. In order to establish contrast in backscattering between the two parts, they are made to be different fromeach other in density and/or crystalline structure. As an alternative,contrast can also be set up between them by featuring, for example, byroughening the surface of the test part irradiated with the primarybeam.

The test part observation method can be applied to a measurement processfor a semiconductor device including at least one of the followingsteps:

a first step is for reading identification information of a specimen andsetting corresponding working command, working conditions and workingdata on the basis of the read identification information;

a second step is for automatically prosecuting designated location,designated time and a designated operation for a designated specimen onthe basis of designated working command, working conditions and workingdata;

a third step is for displaying a plurality of images such as a specimenimage and a three-dimensional configuration simultaneously;

a fourth step is for performing transfer and input/output ofinformation, such as working command, working conditions, working data,detected image data and measured data, on line between the apparatus andexternal units;

a fifth step is for performing alignment and/or positioning between aparticle beam and the specimen;

a sixth step is for measuring the size and/or position coordinates of apattern formed at least on the specimen surface or inside the specimen;

a seventh step is for automatically measuring one or more patternsinside the designated specimen;

an eighth step is for performing retrieval between a measured value ofone or more patterns inside the designated specimen and a presetdesirable standard value to decide whether the pattern is acceptable orunacceptable, and for processing the specimen on the basis of the resultof the decision in accordance with a preset procedure;

a ninth step is for measuring the kind, number and size of a specimenstructure such as a particle or a domain which exists on the specimensurface and/or inside the specimen;

a tenth step is for determining the results of the statistical treatmentof measured values in step 7 and displaying, storing or delivering theresults as necessary;

an eleventh step is for changing the irradiation direction and/or theirradiation angle of the particle beam relative to the specimen;

a twelfth step is for performing at least one of display, storage anddelivery of three-dimensional information on the basis of a plurality ofspecimen images which are observed at two or more designated irradiationangles;

a thirteenth step is for performing at least one of the change ofirradiation energy of the particle beam, particle adjustment such asfocusing needed upon the change of irradiation energy and insuring ofthe same field of view upon the change of irradiation energy;

a fourteenth step is for constructing a tomographic image and/or athree-dimensional image on the basis of a plurality of specimen imagesobserved with two or more particle beams having at least one ofdesignated incident energy level and incident angle and performing atleast one of display, storage, and delivery of the tomographic imageand/or three-dimensional image;

a fifteenth step is for applying at least one of a single or a pluralityof voltages, currents and electrical signals to the specimen;

a sixteenth step is for performing, for the designated specimen, atleast one of the operations of applying a predetermined voltage and/orcurrent and/or electrical signal, fetching a specimen image of adesignated area at a designated time point, comparing a specimen imageof the designated area fetched presently with a specimen image of thedesignated area fetched previously to detect a change, fetching lapsedata of a designated parameter of the specimen at a designated timepoint, and performing display and/or storage and/or delivery of theimage data and/or lapse data;

a seventeenth step is for setting a desired temperature of the specimen;

an eighteenth step is for performing, for the designated specimen, atleast one of the operations of heating the specimen to a predeterminedtemperature, fetching a specimen image of a designated area at adesignated time point, comparing a specimen image of the designated areafetched presently with a specimen image of the designated area fetchedpreviously to detect a change, fetching lapse data of a designatedparameter of the specimen at a designated time point, and performingdisplay and/or storage and/or delivery of the image data and/or lapsedata;

a nineteenth step is for performing, for the designated specimen, atleast one of the operations of fetching a specimen image of a designatedarea and comparing it with a previously designated storage image,extracting a difference between the specimen image and the storageimage, detecting position coordinates of a differing part inside thespecimen, and performing display and/or storage and/or delivery of animage of the differing part and position coordinate data;

a twentieth step is for performing, for the designated specimen, etchingand/or film deposition at a designated single part or a plurality ofdesignated parts inside the specimen;

a twenty-first step is for analyzing, or the designated specimen,analyzing a designated single par or a plurality of designated 10 partsinside the specimen; and

a twenty-second step is for annealing the specimen after it is observedunder the irradiation of the particle beam.

The present invention described thus far has been achieved on the basisof the following novel knowledge acquired by the present inventors.

The present inventors have found that phenomena as below take place inobservation of such a specimen as a semiconductor device conductedusing, as a particle beam, a high-energy scanning electron beam of 50keV or more:

(1) Non-destructive observation of the internal structure of a specimencan be permitted.

Generally, a transmission-type electron microscope is used to observe,for example, the internal structure of a specimen. For observation withthe transmission-type electron microscope, the specimen must take theform of a thin film, and there results destructive observation of thespecimen.

(2) High-resolution observation of an electrically non-conductivespecimen can be ensured without impairing freshness of the specimen.

A scanning electron microscope is used to carry out, for example,high-resolution observation of a specimen configuration. In the case ofobservation of the electrically non-conductive material with thescanning electron microscope, for the sake of preventing degradation ofimage quality due to charge up, a method is adopted wherein gold orcarbon is vapor-deposited on the specimen surface to permit surfaceleakage of accumulated charge, or a low-energy electron beam of about 1keV is used to increase the secondary electron emission amount so as todecrease the charge-up amount.

The vapor-deposition of a conductive film leads to destructiveobservation which impairs the original physical property of thespecimen, and the observation with the low-energy electron beam suffersfrom low resolution.

As a result of analysis of these phenomena, it has been found that theinternal structure can be observed by the present invention inaccordance with the mechanism described below with reference to FIG. 4.

Generally, in a scanning electron microscope, a scanning electron beam101a with an energy ranging from about several hundreds of keV to 30 keVis irradiated to a specimen 102 and, as a result of interaction of theelectron beam 101a with the specimen 102, primary information(reflection electrons 103a, secondary electrons 105a and anelectromagnetic wave 104a representative of X-rays and photons) isgenerated, of which the secondary electrons 105a are mainly used as animage signal to display a specimen image. Of course, X-rays, photons,absorbed electrons or transmitted electrons may be used as an imagesignal.

On the other hand, in the case of a high-energy scanning electron beam101b of the present invention, the electron beam can intrude into thespecimen 102 to reach a part thereof at a large depth owing to the highenergy on the beam, and is then scattered by an internal structure 106to produce scattered (reflection) electrons 103b, which escape from thespecimen 102. When leaving the specimen 102, the scattered electrons103b also interact with the specimen 102 to produce secondaryinformation such as an electromagnetic wave 104b and secondary electrons105b.

When evaluating secondary electrons from the viewpoint of an imagesignal, the secondary electrons 105b representative of the secondaryinformation are richer than the secondary electrons 105a representativeof the primary information. Accordingly, a specimen image based on asecondary electron signal can permit observation corresponding to theamount of scattered electrons 103b which in turn cause secondaryelectrons 105b; that is, observation of the internal structure 106.

FIG. 5 shows a model of the relationship between the scanning electronbeam energy and the secondary electron discharge amount.

Generally, secondary electrons 105b representative of the primaryinformation have a peak emission amount at an energy level aroundseveral hundreds of eV, and, in the energy level range exceeding thatlevel, the emission amount decreases as the energy increases.

On the other hand, secondary electrons 105b representative of thesecondary information will not be discharged before the beam energyexceeds a threshold value Eb. When the energy exceeds Eb, secondaryelectrons 105b begin to discharge and the emission amount increasesgradually as the energy increases.

To explain, when the energy of electron beam 101b is low, electrons 103bback scattered at the test part 106 fail to have energy sufficient toreach the surface of the specimen, and secondary electrons generated ata depth by the scattered electrons 103b likewise cannot escape from thespecimen surface. More specifically, when the depth of the test part 106as measured from the specimen surface is d, the electron beam 101b atenergy E₀ is considered to have a range approximating 2d. The depthallowed for secondary electrons to escape is about 100A and mostsecondary electrons have an energy level of about 10 eV.

On the other hand, the amount of scattered electrons depends on thescattering direction in accordance with the cosine law. Moreparticularly, where an electron beam 101b is vertically incident to aspecimen 102 as shown in FIG. 6, for instance, the amount of scatteredelectrons has a maximum value in a direction at which the scatteringangle θ is 0° and decreases as θ increases to eventually approach 0 atθ=90°. Scattered electrons in a direction at which θ is from 0° to 60°occupy about 90% of the total amount of scattered electrons, andscattered electrons within this range may be considered as an imagesignal.

From the above standpoint, the energy of a scanning electron beam usedin observation of a semiconductor device will be studied below.

Generally, a semiconductor device is composed of an element section of,for example, transistors and capacitors, and a wiring layer formed onthe element section. The device structure has a depth which depends onthe number of wiring layers and which amounts to an average value ofabout 5 μm.

On the other hand, when scattered electrons allowed to contribute to animage signal are considered to be those within a scattering angle rangeof from 0° to 60° in accordance with the above discussion, it can beunderstood from FIG. 7 that the range or length of path of the scanningelectron beam which allows scattered electrons to escape from thespecimen surface must be 15μm or more.

In order to convert a range of 15 μm into the energy of the scanningelectron beam, the following equation by Katz and Penfold (Revs. ModernPhys., Vol. 24:28 (1952)) is used.

    R=0.412E.sup.1.265-0.0954 1n (E/1000) (10 keV<E<3000 kev)

where R is the range (mg/cm²) and E is the energy of the electron beam(keV). The density of the specimen (unit:mg/cm³) is added to this range.

The relationship between the range R and the energy E is shown in FIG.8. The range R is substantially proportional to the square of the energyE².

When the conversion is carried out by using Si of 2.34 g/cm³ density asa typical semiconductor material and Al of 2.69 g/cm³ density as atypical wiring material, the range is about 17 μm in Si and about 15 μmin Al when the energy of the electron beam is 50 keV.

This proves that an electron beam energy level of 50 keV or more isrequired for observation of the semiconductor device. The numericalvalue amounting to 50 keV is sufficiently compatible with practical,empirical observation.

An electrically non-conductive material can be observed under the freshcondition for the reason that most of an electron beam intrudes into aspecimen to reach a large depth thereof or to pass through the specimenand as a result, the charge-up amount near the specimen surface can beminimized.

Contrast of a specimen image to be observed is of a complexity which isnot only attributable to the internal structure of the specimen asdescribed above, but also to the surface structure of the specimen andthe difference in material between parts of the specimen.

For example, when the surface is uneven as shown in FIG. 9, the totalamount and the directional dependency of reflection electrons 103areflected from the specimen surface are different in comparison with thecase where a scanning electron beam 101b irradiates a flat portion ofthe specimen, the case where the irradiation is to a step portion andthe case where the irradiation is to a portion lose to a steppedportion. Thus, differences result for the umber of electrons intrudinginto the specimen which result in scattered electrons 103b, for theamount of secondary electrons generated as an image signal and for theratio between secondary electrons 105a representative of the primaryinformation and secondary electrons 105b representative of the secondaryinformation.

Further, as shown in FIG. 10, the number of electrons intruding into thespecimen which result in scattered electrons, as well as the totalnumber of detectable secondary electrons and the ratio between secondaryelectrons 105a and secondary electrons 105b, are different in comparisonwith the case where specimen materials 102a and 102b are different fromeach other and the case where a foreign material 102c is adhered to thespecimen surface.

Furthermore, even for an embodiment as shown in FIG. 11, where there areshielding structures 102d and 102e against an electron beam 101b, if theshielding structures have a thickness or a depth through which theelectron beam 101b can pass, there is contrast even at normally-shadowylocations D and E, which are irradiated with the transmitting electronbeam, and resulting specimen images can be observed. In other words,this indicates that even in the presence of very large unevenness orprecipitous unevenness on the specimen surface, the interior or bottomof a depression and the side of a raised portion, as well as a surfaceportion shadowed by the raised portion, can be observed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining the principle of observationaccording to the invention;

FIG. 2 is a diagram for explaining a conventional observation method;

FIG. 3 is a diagram showing the relationship between signal intensityfrom a hole and aspect ratio obtained in accordance with theconventional method;

FIG. 4 is a conceptual diagram diagramatically showing the principle ofa scanned specimen image displaying technique of the invention;

FIG. 5 is a graph showing a model of the relationship between thescanning electron beam energy and the secondary electron emissionamount;

FIG. 6 is a conceptual diagram showing an example of distribution of thescattered electron amount;

FIG. 7 is a conceptual diagram useful to determine the electron beamenergy necessary for observation of a semiconductor device;

FIG. 8 is a graph useful to determine the electron beam energy necessaryfor observation of the semiconductor device;

FIG. 9 is a conceptual diagram useful to explain an example of thechange of contrast with conditions of the specimen surface;

FIG. 10 is a conceptual diagram useful to explain another example of thechange of contrast with conditions of the specimen surface;

FIG. 11 is a conceptual diagram useful to explain still another exampleof the change of contrast with conditions of the specimen surface;

FIG. 12 shows results of actual measurement of increased signals fromthe bottom of a hole which are obtained by increasing acceleratingvoltage (energy);

FIG. 13 is a diagram showing the relationship between signal intensityand aspect ratio obtained according to the invention;

FIG. 14 is a diagram for explaining a method of detecting secondaryelectrons generated by reflection electrons from the bottom of a hole;

FIG. 15 is a diagram for explaining a method of observing reflectionelectrons from the bottom of a hole;

FIG. 16 is a diagram for explaining a method of observing bothreflection electrons and secondary electrons simultaneously;

FIG. 17 is a diagram illustrative of detection of electrons transmittingthrough a specimen;

FIG. 18 is a diagram for explaining an embodiment of the invention whichcan permit observation of an object in wafer condition in accordancewith the principle of the observation and detection method according tothe invention;

FIG. 19 is a diagram showing a flow for determining etching conditionsby using the scanning electron microscope;

FIG. 20 is a conceptual diagram of an arrangement in which a specimenchamber is provided in common for microwave etching and for a scanningelectron microscope to facilitate determination of etching conditions;

FIG. 21 is a sectional view showing the construction of a scanningelectron microscope according to another embodiment of the invention;

FIG. 22 is a flow chart showing the operation of a display apparatusaccording to an embodiment of the invention;

FIG. 23 is a conceptual diagram showing an example of a length-measuringmethod according to an embodiment of the invention;

FIG. 24 is a plan view of a specimen;

FIG. 25 is a conceptual diagram showing a method of determining athree-dimensional configuration of a specimen according to an embodimentof the invention;

FIG. 26 is a flow chart for determination of the three-dimensionalconfiguration of a specimen according to an embodiment of the invention;

FIG. 27A is a conceptual diagram showing an embodiment of observation ofparticles in a specimen;

FIG. 27B is a conceptual diagram showing a method of removing a particleon a specimen by etching;

FIG. 28 is a flow chart for observation of particles;

FIG. 29 is a conceptual diagram showing an embodiment of a method fordetermining a crystal direction of a crystal grain in a specimen;

FIG. 30A is a sectional view showing examples of the kind of defectssubjected to defect inspection;

FIG. 30B is a plan view of the defects shown in FIG. 30A;

FIG. 31 is a conceptual diagram showing an embodiment of a method ofperforming defect inspection of a pattern in a specimen;

FIG. 32 is a flow chart of an embodiment of a method for performingdefect inspection;

FIG. 33A is a sectional view showing a pattern in a specimen;

FIG. 33B is a flow chart showing an embodiment of a method of observinga change in configuration of the pattern of FIG. 33A when stress isapplied to the pattern;

FIG. 34 is a flow chart of an embodiment of observing athree-dimensional structure of a pattern in a specimen;

FIG. 35 is a conceptual diagram of an embodiment of observing athree-dimensional structure;

FIG. 36 is a conceptual diagram showing an embodiment of observing asectional area of a pattern in a specimen;

FIG. 37 is a conceptual diagram showing an example of multiplescattering of reflection electrons;

FIG. 38A is a sectional view showing the construction of a prior artobjective lens;

FIG. 38B is a sectional view showing the construction of an embodimentof an objective lens; and

FIG. 39 is a schematic sectional diagram showing the construction andoperation of the embodiment of a specimen.

FIG. 40A is a sectional view showing the principle of signal detectionin another embodiment of the observing method according to theinvention;

FIG. 40B is a sectional view showing a principle of signal detection inthe prior art;

FIG. 41A is a perspective view, partly sectioned, of an essential partof a specimen having a hole structure;

FIG. 41B is a diagram showing a specimen image obtained when the FIG.41A specimen is observed according to the prior art;

FIG. 41C is a diagram showing a specimen image observed according to theinvention;

FIG. 42A is a perspective view, partly sectioned, of an essential partof a specimen having a bank structure;

FIG. 42B is a diagram showing a specimen image obtained when the FIG.42A specimen is observed according to the prior art;

FIG. 42C is a diagram showing a specimen image observed according to theembodiment;

FIG. 43A is a perspective view, partly sectioned, of an essential partof a specimen having an internal structure;

FIG. 43B is a diagram showing a specimen image obtained when the FIG.43A specimen is observed according to the prior art;

FIG. 43C is a diagram showing a specimen image observed according to theembodiment;

FIG. 44A is a perspective view, partly sectioned, of an essential partof a specimen having a conical hole structure;

FIG. 44B shows a specimen image obtained when the FIG. 44A specimen isobserved according to the prior art;

FIG. 44C shows a specimen image observed according to the embodiment;

FIG. 45A shows an image photograph of a semiconductor wafer formed witha resist pattern which is photographed with a scanning electronmicroscope according to teachings of the prior art in connection with aspecimen having a hole structure;

FIG. 45B shows an image photograph of the FIG. 45A semiconductor waferphotographed according to teachings of the present invention;

FIG. 46A shows an image photograph of a semiconductor wafer formed witha resist pattern which is photographed with the scanning electronmicroscope according to teachings of the prior art in connection with aspecimen having a bank structure;

FIG. 46B shows an image photograph of the FIG. 46A semiconductor waferphotographed according to teachings of the present invention;

FIG. 47A shows an image photograph of a semiconductor wafer formed withwiring patterns which is photographed with the scanning electronmicroscope according to teachings of the prior art in connection with aspecimen having an internal structure;

FIG. 47B shows an image photograph of the FIG. 47A semiconductor waferphotographed according to teachings of the present invention;

FIG. 47C shows a schematic sectional view of the semiconductor wafer ofFIG. 47B;

FIG. 48 is a block diagram for explaining still another embodiment ofthe observing method;

FIG. 49 is a block diagram showing the construction of an articledimension measurement SEM for length measurement according to anotherembodiment of the present invention;

FIG. 50 is a sectional view for conceptually showing interaction betweenan electron beam and specimen having an inverted taper surface;

FIG. 51 is a conceptual diagram of an image of the FIG. 50 specimenobtained with the article dimension measurement SEM of the FIG. 49embodiment;

FIG. 52 shows a specimen image obtained with the article dimensionmeasurement SEM of the FIG. 49 embodiment, along with an indication of apair of line cursors adapted to prescribe a range of the articledimension measurement;

FIG. 53 shows an image of a specimen, which has an inverted tapersurface and contains-an isolated line, obtained with the articledimension measurement SEM of the FIG. 49 embodiment, along with anindication of a line profile of signal intensity;

FIG. 54 is a sectional view for conceptually showing interaction betweenan electron beam and a specimen containing an internal isolated line;

FIG. 55 is a conceptual diagram of an image of the FIG. 54 specimenobtained with the article dimension measurement SEM of the FIG. 49embodiment;

FIG. 56 is a conceptual diagram showing a line profile of signalintensity in an image of a specimen having a taper surface andcontaining an isolated line;

FIGS. 57A and 57B are sectional views showing an isolated line having anon-inverted taper surface and another isolated line having an invertedtaper surface, respectively;

FIG. 58 is a graph showing a ratio of intensity between signalsindicative of an inverted taper surface and a non-inverted tapersurface;

FIG. 59A shows an image of an obliquely placed rectangularparallelepiped obtained with the article dimension measurement SEM ofthe FIG. 49 embodiment;

FIG. 59B is a diagram showing an inclined pattern of the rectangularparallelepiped having a rectangular cross-section;

FIG. 60 is a block diagram showing the construction of an articledimension measurement SEM for length measurement according to stillanother embodiment of the present invention;

FIG. 61 is a block diagram showing details of the construction of athree-dimensional (cubic) model generator included in the FIG. 60 SEM;

FIG. 62 is a diagram showing a scanning image, obtained using a lowenergy electron beam, of a contact hole having an inverted tapersurface;

FIG. 63 is a diagram showing a three-dimensional model;

FIG. 64 shows an illustration of the three-dimensional model along withthe scanning image;

FIG. 65 shows the three-dimensional model illustration on which thescanning image is superimposed;

FIG. 66 shows an illustration of a three-dimensional model which ismodified to match the scanning image;

FIG. 67 is a conceptual diagram showing an article dimension measuringmethod using the modified three-dimensional model illustration; and

FIG. 68 is a conceptual diagram similar to FIG. 67.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

When a hole in SiO₂ having an aspect ratio of about 3 and a depth of 1.5μm was observed, the ratio between signals from the bottom and thesurface was measured by changing energy of a primary electron beam toobtain results is shown in FIG. 12. Namely, the ratio between secondaryelectrons generated by reflection electrons, and secondary electronsgenerated by the primary electron beam, was measured. It will beappreciated that the ratio is maximized around 100 kV electron beamenergy. When the primary electron beam has low energy, reflectionelectrons are absorbed by the side wall and therefore no secondaryelectrons are generated by the reflection electrons. As the energy ofthe primary electron beam increases, the number of reflection electronspenetrating through the side wall increases and hence the number ofsecondary electrons thereby generated is increased gradually. However,as the energy is further increased, the primary electron beam intrudesinto the specimen more deeply and the number of reflection electronsdecreases, leading to a decrease in the number of secondary electrons.This is the reason for existence of the maximum value. Electron beamenergy corresponding to the maximum value is related to the depth andmaterial of the hole. The deeper the hole and the denser the material,the higher the maximum value becomes.

FIG. 13 shows the relation between the aspect ratio and the signal ratioobtained when a deep hole was observed by using 100 keV energy. Therelation obtained with 1 keV is indicated for reference and it will beappreciated that with 100 keV, even when the aspect ratio exceed 3, thesignal ratio does not decrease and holes of higher aspect ratios can beobserved.

In the conventional scanning electron microscope, the energy is lessthan 50 keV and high energy exceeding 50 keV is not used. This isbecause there was no concept of observation grounded on the principledescribed herein. Effectiveness of the high-energy primary electron beampermitting observation of deep holes is disclosed herein for the firsttime.

FIG. 14 shows a method of detecting secondary electrons generated byreflection electrons of high energy. This method uses a scintillator 10and a secondary-electron multiplier 12. Supplied to the scintillator 10is a high voltage of 10 kV from a high voltage power supply 13. By usingan attraction electric field 9 formed by the high voltage, secondaryelectrons generated by the reflected elections in the surface of aspecimen 8 are detected. A primary electron beam 4 having energysufficient to generate the secondary electrons from reflection electronsis focused and irradiated on the specimen 8 by means of an objectivelens 7. In the Figure, circuits for scanning the primary electron beamand for displaying scanning images are omitted.

FIG. 15 shows an example of detecting not secondary electrons butreflection electrons transmitting through the side wall. A reflectionelectron detector 15 having a large view angle relative to a specimen 8is interposed between an objective lens 7 and the specimen 8. Thereflection electron detector 15 may be a semiconductor detector having aPN-junction or a Schottky junction or may be based on a method ofcausing phosphors to luminesce, and of detecting luminescence (anexample using a semiconductor is shown in the embodiment). Since theenergy of reflection electrons is high, the surface layer of thesemiconductor detector is made to be thick (1 to 10 μm), thus preventingdegradation of detection efficiency. In the case of phosphors, similarthickening is also employed. The thickness of the phosphor layermeasures 10 to 100 μm, depending on energy.

FIG. 16 shows an example where reflection electrons and secondaryelectrons are both detected. An attraction electrode 16 is providedwhich passes through the center of an objective lens 7. Secondaryelectrons 5 generated by the reflection electrons from a specimen 8 aredrawn into a magnetic field of the objective lens 7 and pulled upwardsby means of the attraction electrode 16. The secondary electron 5 thuspulled upwards are accelerated by an attraction electric field 9 formedby a scintillator 10 so as to impinge on the scintillator 10 and causeit to luminesce.

Luminescent light is guided to a light guide 11 and amplified andconverted into an electrical signal by means of a secondary-electronmultiplier 12. Reflection electrons generated from the specimen 8 havehigh energy and therefore they are hardly deflected by an electric fieldformed by the attraction electrode 16, keeping a substantially straightpath and impinging upon a reflection electron detector 15. Through thisprocess, the reflection electrons themselves and the secondary electronsgenerated from the reflection electrodes can be detected distinctively.Since scanning images formed by the two types of electrons are slightlydifferent from each other, it is possible to select one of the imageswhich has better contrast, or to perform addition/subtraction to improvecontrast.

In the foregoing embodiments, secondary electrons and reflectionelectrons are generated on the side upon which the primary electron beamis incident, but, when the specimen is thin, either secondary electronsgenerated by transmitted electrons or the transmitted electronsthemselves may be detected.

FIG. 17 shows an embodiment in which secondary electrons generated onthe side opposite the primary electron beam and transmitted electronsare detected. The manner of detection on the primary electron beam sideis the same as that in the previously-described embodiment. Secondaryelectrons 20 generated from the undersurface of a specimen 8 byelectrons transmitting through the specimen and secondary electrons 21generated by impingement of transmitted electrons 19 upon a reflectionplate 22 are detected by using a scintillator 10, a light guide 11 and asecondary-electron multiplier 12. Electrons, of a primary electron beamof 200 keV energy have a range of 200 μm and can transmit through even aSi wafer used in the semiconductor industry. Thus, by detectingtransmitted electrons and secondary electrons generated from theundersurface of the specimen, a hole formed in the surface of thespecimen 8 can be observed.

FIG. 18 shows a scanning electron microscope using the principle ofobservation and the detection method described previously. The source ofelectrons can lead a single crystal of LaB₆ heated to emit electrons.Emitter electrons are controlled by means of a Whenelt 24. The emittedelectrons are accelerated by accelerating electrodes 25. Theaccelerating voltage (energy) in the present embodiment has a maximumvalue of 200 keV.

An accelerating electrode 25 of the uppermost stage is applied with theaccelerating voltage, and divisional voltages due to dividing resistors34 are applied to individual accelerating electrodes 25. Here, the cableand power supply for application of the accelerating voltage areomitted.

An accelerating unit including the accelerating electrodes 25 isshielded with a high voltage shield 35. An accelerated primary electronbeam 4 is reduced in size by means of a first condenser lens 26, asecond condenser lens 27 and an objective lens 7. When an objective lenshaving a focal distance of 30 mm is used, a resolution value of 3 nm canbe obtained at 200 keV. The aperture of the electron beam is determinedby an aperture 36 placed on the second condenser lens 27.

Scanning of the electron beam is carried out by a scanning coil 28. Thescanning coil is constructed of two stages of coils so that the electronbeam subject to scanning may pass through the center of the objectivelens 7. Reflection electrons reflected at a specimen are detected by areflection electron detector 15 and secondary electrons generated by thereflected electrons are led upwardly of the objective lens 7 anddetected by a detecter comprised of a scintillator 10, a light guide 11and a secondary-electron multiplier 12.

The specimen is a wafer of 4 inches or more carried on an XY finemovement stage 29. The specimen an be inclined by ±15 degrees in desireddirections by mean of a specimen inclination fine movement section 30.The specimen inclination fine movement section 30 has three posts, andthe length of each post can be controlled by computer. A wafer to beobserved is contained in a dedicated cassette 32 and the cassette isstored in a preparatory chamber 33. When conducting an observation, avalve 34 is opened and the specimen is brought onto the XY fine movementstage 29 by using an exchange mechanism (not shown). When the sameportion of the specimen is observed by changing the inclination angle,the height can be measured (stereo-measurement).

In highly integrated semiconductor devices, the etching process forworking a deep hole of high aspect ratio is important as has alreadybeen described. Etching for working a deep hole of high aspect ratio isvery difficult and for determination of etching conditions, observationof the bottom of the deep hole and confirmation of the process ofetching are needed.

FIG. 19 shows a flow of the confirmation wherein in accordance with theresults of confirmation, feedback for urging, for example, re-etching isundertaken to ensure process integrity. The thus-determined etchingconditions are relayed to the succeeding process. By repeating theconfirmation at a fixed period, the process can be made to be stabler.

The scanning electron microscope is very effective for the confirmationof etching and can contribute to improvement in yield of production ofhighly-integrate devices. Especially, the high-energy scanning electronmicroscope utilizing secondary electrons generated byreflected/transmitted electrons described so far is effective.

FIG. 20 shows an arrangement contrive to simplify the aforementionedconfirmation process, in which a specimen chamber is provided in commonfor a microwave etching apparatus 38 and a high-energy scanning electronmicroscope 37, and etching and inspection can be carried out alternatelyby merely moving a specimen from an etching apparatus specimen stage 39to a scanning electron microscope XY fine movement stage 42. The degreeof vacuum in the microwave etching apparatus is 10⁻⁴ Tor which iscomparable to that in the scanning electron microscope but, because ofthe use of inert gas, an intermediate chamber 41 is provided in thepresent embodiment in order that the inert gas can be prevented fromflowing into the scan mg electron microscope by switching valves 40alternately for intermediate chamber 41. In the Figure, the evacuationsystem is omitted.

As described above, in accordance with the principle of observationaccording to the invention, deep holes of which observation wasimpossible in the past can be observed. This implies that inspection canbe carried out in-line in the process of semiconductor deviceproduction, resulting in very beneficial effects.

Another embodiment will be described with reference to FIG. 21.

Firstly, a specimen 102 is moved from a loader/unloader chamber 120 ontoa specimen stage 121 inside a specimen chamber 122 by a load/unloadmechanism, not shown, and loaded on the specimen stage. Theloader/unloaded chamber 120 is in the form of a load lock mechanism,wherein the loader/unloader chamber is separated from the specimenchamber 122 by a vacuum valve 123 so that the specimen 121 may be loadedon the specimen stage 121 without breaking vacuum. An electron beam 101bis then emitted from an electron gun 115 and it is accelerated to anenergy level of several tees of keV by means of an accelerating tube116, focused to be thinned by means of a focusing lens 117 and anobjective lens 118, and irradiated to the specimen 102. When subjectedto XY deflection by means of a deflector 119, the electron beam isscanned on the specimen 102.

A mechanism for moving the specimen and the specimen stage 121 isprovided, and may be an external view inspection apparatus (trade name:S-7000) manufacture and sold by Hitachi, Ltd. The electron gun 115,accelerating tube 116 and focusing lens 117 are structurally the same asthose of a transmitting electron microscope (trade name: H-800) alsomanufactured and sold by Hitachi, Ltd.

Secondary electrons 105b are discharged or emitted from a portion of thespecimen irradiated with the scanning electron beam 101b, along with anelectromagnetic wave 104b representative of X-rays and photons.

Secondary electrons 105b are drawn upwards in the axial direction of theobjective lens 118 while whirling under the influence of a magneticfield of the objective lens 118, and are detected by a secondaryelectron detector 124 constructed of a scintillator and aphotomultiplier tube so as to be converted into an electrical signal.The electrical signal is amplified and then modulated in brightness bymeans of a signal amplifying/processing unit 125 to produce a specimenimage which is displayed on a display 126. Similarly, electromagneticwave 104b, such as X-rays or photons, discharged from the specimen 102is detected by a detector 127 and used for analysis or image display.

The specimen stage 121 includes an X/Y moving mechanism 121a and arotating/inclining mechanism 121b to permit selection of a desiredobservation site or location and a desired observation direction.

FIG. 22 shows an example of a flow chart of scanning and processing inthe case where semiconductor wafer specimens 102 are processed in lotunits.

Wafer specimens 102 are kept by lot in a wafer carrier. When the wafercarrier is set in the loader/unloader chamber 120, a lot numberdescribed on the wafer carrier is read by means of an optical ormagnetic reader and the apparatus is started. Subsequently, workingcommand, working conditions and working data corresponding to the lotnumber are read. The succeeding process is automatically carried out onthe basis of the working command, working conditions and working data.

The working command stipulates the processing operation that determineswhich one of the wafers is to be subjected to which operation at whichsite. The working conditions are concerned with electron beamirradiation, image forming process and measuring process, and prescribeapparatus parameters necessary for performing the various operations.The working data correspond to data other than the apparatus parametersneeded for work prosecution, for example, position coordinate data ofdefects transferred from an external tester or a defect inspectionapparatus.

In the processing, a sheet of a designated wafer is first loaded on thespecimen stage 121. Subsequently, wafer aligning work is carried outaccording to the alignment method adopted in an electron beam exposureapparatus. Rough alignment of the wafer may be conducted before loadingthe wafer on the specimen stage 121. For example, a method may beemployed wherein a contour of the wafer is detected optically todetermine the center of the wafer. For fine alignment of the wafer, amethod may be employed wherein an electron beam 101b is scanned on analignment mark formed on the wafer to produce reflection electrons, andan alignment mark position is determined from a signal waveformrepresentative of the thus-produced reflection electrons. Alternatively,an alignment mark position may be determined by bringing a scanningimage of an alignment mark into coincidence with a previously storedreference image.

After completion of the alignment, another work of interest, such asobservation, inspection and measurement or analysis is carried out.These operations may be conducted individually or simultaneously; forexample, observation and analysis may be conducted in combination. Workresults as represented by image data, inspection data, measurement dataand analysis data of the specimen are then subjected to predetermineddata processing and thereafter kept and displayed in accordance with apredetermined procedure, or are transferred to an external hostcomputer, analysis apparatus or wafer process apparatus.

Various operations can be practiced in such a way that a plurality ofdesired sites within a wafer are worked, or the same site on o in awafer is worked repetitively at desired time intervals.

Further, the particular operations can be changed for individual wafersor for individual working sites on or in a wafer. The type of operationcan be inputted through a control computer of the present apparatus orfrom a host computer on line.

The above operations are applied to all of the designated wafers.

Specific examples of work of interest or the present work will now bedescribed.

One of the inspection operations is a length-measuring operation. Anexample of this working is shown in FIG. 23.

A pattern 107a formed on the surface of a specimen 102 and a pattern107b formed inside the specimen are scanned with an electron beam 101b,and pattern dimensions W and W', interpattern distance D and patternposition coordinates P and P' are determined from secondary electronsignal waveforms. Length measurement is carried out in a specific mannerwhich accords with a method generally employed in a length-measuringSEM. The electron beam 101b has an energy level of 50 keV or more.Therefore, as will be seen from the relation depicted in FIG. 5, asignal corresponding to a first pattern 107b is larger than a signalcorresponding to a second pattern 107a.

In this case, if, as shown in FIG. 24 the pattern 107a is located sonear the pattern 107b to be measured that a scanning line 101s of theelectron beam encounters the pattern 107a as shown at A, errors inmeasurement possibly occur. It is desirable that at a length measuringportion the patterns 107a and 107b be spaced apart from each other by awidth of a scanning line or more as shown at scanning line 102s.

As exemplified in FIGS. 25 and 26, the same view field can be observedat different angles or in different directions to obtain two or moreimages of the same field of view, thus determining a three-dimensionalconfiguration, and display of the three-dimensional configuration ormeasurement of three-dimensional size can be effected on the basis ofthe three-dimensional configuration. For example, images of the sameview field are fetched at an irradiation angle of 0° subtended by theelectron beam 101b and specimen 102 (observed from directly above) andat an irradiation angle of α subtended by the electron beam and specimen(observed obliquely from above), and the two images are examined with adistance difference between two points to be measured to calculate athree-dimensional configuration. Specifically, in a specimen image at anirradiation angle of 0°, a distance between two points in the horizontaldirection is taken as an actual measure but a distance in the verticaldirection is taken as 0 (zero).

On the other hand, utilized in connection with a specimen image at anirradiation angle of α is the fact that the actual size is taken ascontracted by x cos α in the horizontal direction and x sin α in thevertical direction.

The irradiation angle can be changed by changing the incident angle ofelectron beam 101b to that specimen 102 by means of a deflector or bychanging the inclination angle of specimen stage 121. The change ofirradiation direction and angle is not limited to the two-step change.When a specimen is inclined in a number of directions in which thespecimen is desired to be observed in configuration and to be measuredin length, and a number of specimen images are fetched, fidelity andaccuracy of a three-dimensional configuration to be calculated can beimproved. By narrowing the width of scanning of the electron beam, asubstantial sectional view can be formed accurately.

A plurality of images can be displayed simultaneously by, for example,displaying a specimen image and a three-dimensional image incombination. The simultaneous display can be provided on the samedisplay or on different displays.

This function can be applied, in particular, to a pattern size measuringapparatus, a pattern position coordinate measuring apparatus, anapparatus for accurate measurement of pattern superimposition and anapparatus of measurement of pattern drawing distortion or transferdistortion.

Especially, the conventional applied electron beam apparatus was unableto measure a pattern positioned inside a specimen and failed to measurethe accuracy of pattern superimposition, but the present embodimentmakes both possible.

As a second example, measurement of particles and domains, bubbles andforeign materials is enumerated.

FIG. 27A shows an example of measurement of particles according to themethod illustrated in FIG. 28. A designated area of specimen 102 isscanned with a scanning electron beam 101b to fetch specimen images. Thespecimen images are analyzed and the number of particles are counted todetermine data indicative of size distribution and distribution ofparticles within a wafer. In this case, the number of counted particlescan be analyzed in a manner which accords with the method generallyemployed in an image analyzer.

A measuring operation can be carried out along with analysis ofcomponents of particles. Used for the component analysis is a methodwherein position coordinate data of a particle 108c desired to besubjected to component analysis is determined from a specimen image,positions of the electron beam and of the particle to be analyzed aredetermined on the basis of the position coordinate data, the electronbeam 101b is irradiated onto the target particle 108c and characteristicX-rays 109 emitted from the particle 108c are detected to determine acomponent. A semiconductor detector is used for X-ray detection and atechnique is employed wherein the kind and quantity of an element aredetermined from the peak value and number of current pulses generated byincident X-rays.

In this procedure, for the sake of increasing sensitivity and accuracyof the component determination a covering on the particle 108c may beremoved. Selective removal of the covering on the particle can beachieved by, for example, laser-assist etching as shown in FIGS. 27B and28, in which an etching gas 112 is sprayed from a gas nozzle 111 while afinely focused laser beam 110 is irradiated to a portion desired to beetched away. The etching gas is a gas having selectivity for etchingonly the covering without impairing the particle.

When the target consists of various kinds of specimens, a plurality ofgas nozzles are adopted and a proper kind of gas is selectively used.

In order to optimize the etching conditions, the horizontal position andvertical position of the gas nozzle are designed to be adjustablymovable and the direction of gas spraying is made to be adjustable.

Obviously, for the component analysis, such information as an Augerelectron beam or cathode luminescence may be detected in place ofX-rays. In addition to an electron beam, a laser beam or an ion beam maybe used as an exciting beam for use in the analysis.

As for the etching method, other chemical etching methods may be used.For example, an ion beam-assist etching and a physical etching methodsuch as ion beam sputtering may also be employed. Generally, however,because of the necessity for securing high selectivity of etchingbetween the covering and the particle, the chemical etching method issuitable.

Even in the particle measurement, by fetching a plurality of specimenimages in different irradiation directions and at different irradiationangles and subjecting the fetched images to a three-dimensionalconfiguration processing, information in the direction of depth as to athree-dimensional configuration of a particle or as to what kind ofparticle is distributed at which depth position can be obtained.

When a specimen is observed by changing the irradiation direction andangle, knowledge of the direction of a crystalline structure can also beobtained. FIG. 29 shows an example to this effect.

Illustrated in the figure is an instance where a specimen 102 has apolycrystalline structure 106 (internal structure) and the crystaldirection is oblique in a crystal grain 106a, vertical in a crystalgrain 106b and horizontal in a crystal grain 106c. When the specimen isobserved with a scanning electron beam 101b from directly above, theamount of scattered electrons 103b directed to the specimen surface,that is, the image signal amount is the largest for the crystal grain106c and is decreased, in order, for crystal grains 106a and 106b. Onthe other hand, when observation is carried out with a scanning electronbeam 101b' irradiating in an oblique direction, the image signal amountdecreases in the order of crystal grains 106c, 106b and 106a.

In this manner, the image signal amount or image contrast changes inaccordance with the relation between crystal direction and observationdirection. By analyzing the condition of this change, the crystaldirection of each crystal grain can be decided. Through image analysis,as in the case of particle number counting, data of crystal grain sizedistribution and data of crystal direction distribution can be obtained.

Enumerated as a third example is inspection of pattern defects andforeign matter. There are various kinds of defects as exemplified inFIGS. 30A and 30B. FIG. 30A is a sectional view of a specimen and FIG.30B is a plan view of the specimen. In order to detect these defects,the procedure shown in FIGS. 31 and 32 is performed, which accords witha technique used in a general defect inspection apparatus.

A specimen image of a designated areas first fetched and subjected toimage processing such as smoothing, and thereafter the alignment andcomparison of the specimen image with a previously stored referenceimage is effected to provide a difference between the specimen andreference images, and a defect/foreign matter is detected from thedifference. In FIG. 31, a portion B is detected as a raised defect.

The reference image may be either a standard specimen image taken withinan area corresponding to a designated area of an identical specimen orwithin the same kind of specimen, or a pattern data image of thecorresponding area prepared on the basis of pattern data. In theinspection operation, the reference image can partly be defined by astandard specimen image, and partly by a pattern data image. Theseimages may be used in combination.

The entire surface of a wafer may be used as an inspection area, or onlypart of the wafer surface may be inspected. For example, positioncoordinate data of a chip or a circuit block, which have been decided tobe unacceptable or defective through inspection based on a tester or adefect inspection apparatus, are inputted from the tester or the defectinspection apparatus on line, positions of the unacceptable chip orcircuit block are determined from the inputted coordinate data, and onlya portion in question is selectively subjected to defect inspection. Onthe other hand, even in the defect inspection, component analysis of thedefective portion can be effected, as in the case of the example ofparticle measurement.

By using a technique similar to the removal of a covering by an etchinggas, a pattern defect can be corrected. In contrast, however, to theremoval of a raised defect or an isolated defect, wherein an etching gasis used, a sedimentary gas is used for correction of a depressiondefect. Essentially, the defect correction technique is the same as thatperformed by a photomask defect correction apparatus or an LSI wiringcorrection apparatus.

While the conventional defect inspection apparatus is in general of theoptical type, the defect inspection based on a high energy electron beamis advantageous in that not only the defect detection sensitivity ishigh but also a defect underlying an opaque material can be detected. Inparticular, of the defects shown in FIGS. 30A and 30B, detection of apattern position shift would be impossible with the conventional method,but possible with the inventive method based on the high energy electronbeam.

A fourth example is for monitoring a change in state of a specimen. FIG.33A is a sectional view of an exemplary wiring pattern 107 embedded inthe specimen. FIG. 33B shows, as an example, an application of thesemiconductor device specimen to an accelerating test.

A probe 113 is put on opposite ends of the wiring pattern 107 to bemonitored and a stress current is applied from a current source 114 tothe wiring pattern through the probe 113. A specimen image of the wiringpattern 107 is fetched at designated time intervals and the state ofwiring pattern 107 ultimately ending in breakage is recorded anddisplayed. For example, a difference between the preceding state and thepresent state is displayed to emphasize only a change. Simultaneouslywith the specimen image, lapse of electrical parameters such as currentvalue and resistance value are collected, recorded and displayer. Ofcourse, the number of probes and power supplies used can be increased inaccordance with the number of wiring conductors to be monitored.

The stress applied is not limited to DC current but may also be ACcurrent or pulse current. In addition to current, voltage or anoperating electrical signal may be applied to the specimen, or thespecimen can be heated or cooled to observe and monitor a change due totemperatures. In the case of heating, noises attributable to thermionsor radiation from a heating unit adversely affect an image signal andmust be compensated. The plurality of kinds of stress as above may beapplied in combination or one at a time. A mechanism for applying thestress to the specimen accords with that used in observation with theconventional scanning electron microscope.

A fifth observation technique is for tomographic observation. This typeof observation takes advantage of the fact that information obtained inthe direction of depth of a specimen changes depending on the energy ofthe electron beam.

FIG. 34 shows an example of a process flow. Specimen images aresequentially fetched while changing the acceleration voltage of theelectron beam.

The acceleration voltage is first set. Then the electron beam isadjusted and the same field of view is settled. The electron beamadjustment is fulfilled by performing axial alignment, focusing andcorrection of astigmatic aberration in order to maintain high-resolutionconditions. Settlement of the same field of view aims at permitting anarea of the same field of view to be always observed even when theacceleration voltage is changed. For example, a method is employedwherein a specimen image previously fetched is used as a referenceimage, and the scanning area of the electron beam is adjusted to allowthe specimen image currently under observation to coincide with thereference image. Alternatively, according to the alignment system usedin the electron beam exposure apparatus, alignment can be accomplishedby using an object with a designated image in place of an alignmentmark.

Subsequently, a specimen image within a designated area is fetched. Thehigher the set acceleration voltage, the deeper a portion from whichinformation contained in the fetched specimen image is obtained becomes.

For example, an instance is considered where, as shown in FIG. 35,wiring patterns 107b, 107b' and 107b" are inside a specimen 102.

If the set acceleration voltage is relatively low and a scanningelectron beam 101b intrudes to a depth d, reaching the vicinity of thewiring pattern 107b, the wiring pattern 107b can be seen in a specimenimage A but the wiring patterns 107b' and 107b" located at deeper levelscannot be observed.

On the other hand, when a relatively high acceleration voltage isapplied and the electron beam 101b' intrudes to a depth d', reaching thewiring patterns 107b' and 107b", the wiring patterns 107b' and 107b" canbe observed in a specimen image A' obtained.

Accordingly, by preparing a difference image between the specimen imagesA' and A, a tomographic image A' in the vicinity of the depth d', thatis, images of only the wiring patterns 107b' and 107b" can be obtained.By combining a plurality of tomographic images obtained in this manner,a three-dimensional configuration inside the specimen can be obtained.

Usually, the signal level and the degree of contrast are different forthe specimen images A and A'. Therefore, in order to obtain a highlyaccurate difference signal, the signal level and contrast degree of thespecimen image A must be overlapped with those of the specimen image A'in a pre-process.

FIG. 36 shows an example of the pre-process needed for determination ofa difference signal. Image signals of the specimen images A and A' arefirst ANDed. In the AND process, each pixel of the image A is comparedwith each pixel of the image A' to determine the presence of an image,to provide a portion C where an image signal of only the A image existsand a portion D where signals of both the and A' images exist. In thiscase, the portion C corresponds to the wiring pattern 107b' and is usedto provide a signal indicative of a tomographic image.

On the other hand, in the portion D, a signal level overlap process anda contrast overlap process are effected and then subtraction is carriedout between the overlapped signal levels and between the overlappedcontrast degrees. A difference signal E obtained by the subtractioncorresponds to the wiring pattern 107b" and is used in combination withthe signal at the portion C to provide a signal indicative of thetomographic image A'.

In the embodiments shown in FIGS. 35 and 36, the incident energy of theprimary beam is changed. Additionally, by changing the incident angle ofthe primary beam as shown in FIGS. 25 and 26, a tomographic image or athree-dimensional image of the pattern can be formed with higheraccuracy.

When a semiconductor device is irradiated with the electron beam, therearises a problem that the device is damaged by the irradiation. Theirradiation damage degrades characteristics of the device, and thereforeit is necessary that the damage should be mitigated or a damaged portionshould be recovered.

The causes of the irradiation damage have been studied to find thatreflection electrons 103 of high energy undergo multiple scattering, asshown in FIG. 37, in a space between the specimen 102 and the undersideof the objective lens 118 arranged above the specimen. The multiplescattering is a major cause of heavy damage.

FIGS. 38A and 38B show enlarged sectional views of a specimen and anobjective lens portion and are useful to study countermeasures againstthe multiple scattering of reflection electrons.

Conventionally, as shown in FIG. 38A, a vacuum shield pipe 128 made ofphosphor bronze passes through an electron beam path defined by an upperpole piece 118a and a lower pole piece 118b of the objective lens.However, phosphor bronze has a large reflection coefficient and isliable to cause the multiple scattering.

FIG. 38B shows a technique of suppressing the multiple scattering ofreflection electrons. A specimen-opposing portion 128a of vacuum shieldpipe 128 facing the specimen 102 is made of carbon, which is a lightelement having a small reflection coefficient for electrons. Thespecimen-opposing portion 128a has a sawtooth-shaped sectional form,which inhibits multiple scattering of reflection electrons.

The material of the specimen-opposing portion 128a may also be a lightmetal material such as aluminum. The sawtooth-shaped form is notlimitative and the portion 128a may have a different non-flat form, suchas a comb form.

As for recovery of a portion suffering an irradiation damage, it hasbeen confirmed that the threshold value of a MOS device shifted underthe irradiation of an electron beam during observation can recover byannealing with hydrogen at 450° C. After observation, the specimen mustbe annealed in accordance with its application. Most preferably, theanneal process is performed immediately after observation of thespecimen.

The annealing function can be fulfilled by using a heating mechanismprovided to the specimen stage 121, a heating mechanism additionallyprovided to the loader/unloader chamber 120 or a separate unit. Heatingmay be of the resistance-heating type or the lamp-heating type, and agas such as hydrogen or nitrogen may be admitted to an annealing processunit.

While the foregoing embodiments use a system wherein the secondaryelectron detector 124 is arranged above the objective lens 118 andsecondary electrons are collected by utilizing a magnetic field of theobjective lens, a different system may alternatively be employed whereina secondary electron detector is arranged under an objective lens toapply an electric field by means of which secondary electrons aredetected.

In place of the scintillator and photomultiplier tube, asecondary-electron multiplier may be used as the secondary electrondetector.

X-rays, photons or absorbed electrons, other than the secondaryelectrons, may be detected as the secondary information which is used asa signal.

In order to increase the signal amount of the secondary information, asubstance liable to generate secondary electrons or fluorescence may bedeposited or coated thinly on a specimen to be observed. FIG. 39 shows aexample to this effect. An oxide material having a high secondaryelectron emission efficiency is deposited thinly on a specimen 102 toincrease the number of secondary electrons generated by scatteredelectrons 103b. In an alternative, a fluorescent material substitutingfor the oxide material may be coated thinly on the specimen so thatscattered electrons may cause the fluorescent material to generatefluorescence, which in turn is detected.

The specimen is not limited to a wafer, but any device built in apackage may be used as a specimen.

Specimens have been described as treated in by lot, but this is notlimitative and specimens may be treated sheet by sheet. The specimen hasbeen described as mounted or dismounted manually by the operator, butinstead it may be conveyed automatically to another processing unit.

Movement, rotation and inclination of site of a specimen to be observedhave been described as being effected by moving, rotating and incliningthe specimen stage, but alternatively they can be accomplished by movingthe irradiation position of an electron beam, rotating the electron beamirradiation area and inclining the electron beam irradiation direction.

In addition to an electron beam, other exciting beams such as an ionbeam and a laser beam may be used as the particle beam.

In addition to scattered electrons, a electromagnetic wave may be usedas the primary information for producing the secondary information.

The target specimen is not limited to a semiconductor device, but may bea photomask substrate, a display device, a wiring board, an opticaldisc, a metal material, a polymer material or a living body. With theaim of increasing contrast, such a light element as a living body can bedyed with a heavy metal.

Effects brought about by typical features of the present inventiondisclosed in the present application will be described briefly asfollows.

According to the present invention, by utilizing the newly-foundphenomena described above, conventionally-considered difficulties orimpossibilities can be solved with ease. Beneficial applications will beexemplified below.

From the viewpoint of non-destructive observation, attainable advantagesare: (1) structure, defects and foreign matter inside a specimen can beobserved, (2) surface structures having greater and more precipitousunevenness than that observable with the prior art can be observed, (3)three-dimensional configurations of the surface and internal structurescan be determined, (4) tomographic observation can be ensured, and (5)an electrically non-conductive material can be observed with higherresolution according to the present invention than in the prior art.

From the viewpoint of non-destructive inspection and measurement,attainable advantages are: (1) length and height of a pattern orstructure formed inside a specimen or on the surface thereof can bemeasured, (2) particles, domains, bubbles and foreign materials presentinside a specimen or on the surface thereof can be counted and measured,(3) pattern defects and foreign matter present inside a specimen or onthe surface thereof can be inspected, (4) lapse of a change in thestructure inside a specimen or on the surface thereof can be monitoredon the spot, and (5) length can be measured with higher accuracy, anddefects and foreign matter can be inspected with higher sensitivity inthe present invention than in the prior art.

In defect inspection, work can be done more efficiently by usingcomponent analysis and defect correction.

When used in combination with another processing apparatus, the presentapparatus can also be utilized as an in-line process monitor.

Further, since applications of the present techniques can solveimpossibilities and difficulties, as previously considered, devices andparts of higher quality and higher reliability can be manufacturedeconomically.

Another embodiment of the observing method will be described withreference to FIG. 40A. The previously-described scanning electronmicroscope can be used as an observing apparatus. Obviously, a chargedarticle beam may be used in place of an electron beam.

The observing method of the present embodiment is for providing such asuperimposed display that specimen image of a part of a specimen whichis unseen in the direction of irradiation of an electron beam issuperimposed on a specimen image of a part of the specimen which is seenin the direction of irradiation of the electron beam. In the observingmethod, an electron beam 202a for scanning a specimen 201 is irradiatedthereon to interact with the specimen 201 to thereby generate secondaryelectrons 203 and secondary electrons 203a, and an image signalindicative of the secondary electrons 203 and an image signal indicativeof the secondary electrons 203a are used to form a specimen image.

In this case, the electron beam 202a is used at a higher speed than anelectron beam used in the prior art in order that a signal indicative ofordinary secondary electrons 203 and a signal indicative of secondaryelectrons 203a generated by reflection electrons scattered in the insideof the specimen 201 are employed as they are to provide a superimposeddisplay of a specimen image of a part of the specimen which is unseen inthe direction of irradiation of the electron beam 202a and a specimenimage of a part of the specimen which is seen in the direction ofirradiation of the electron beam 202a, and so can be displayed accordingto the prior art. The energy of the electron beam 202a is suitablyselected in accordance with the material an structure of the specimenand may preferably be, for example, 50 KeV or more. More preferably, itmay be 100 to 200 KeV.

In the specimen having the structure of FIG. 40A and made of siliconoxide, a hole has a diameter of 0.4 μm and a depth of 1.5 μm and aninternal structure 209 is a line made of tungsten which is buried at adepth of 0.6 to 1.2 μm measured from the specimen surface. When such aspecimen was irradiated with an electron beam 202a at 100 KeV, thespecimen surface and the shapes of hole bottom 208 and line 209 could beobserved at the same time.

The operation of the present embodiment will now be described by makinga comparison with that of the prior art.

In the prior art, an electron beam 202 at a relatively low speed(typically at 0.5 to 20 KeV) is used and as a result, portions shadedfrom the electron beam take place as shown in FIG. 40B and secondaryelectrons 203a due to electrons reflected at the hole bottom 208 andinternal structure 209, standing for the shaded portions, are notgenerated or are generated in a very small amount, making it impossibleto observe images of these shaded portions.

In contrast, when an electron beam 202a at a high speed as in thepresent invention is used, the irradiated electrons have sufficientkinetic energy and as a result, the electron beam 202a can penetratethrough the specimen 201, can be reflected at the hole bottom 208 andinternal structure 209 and eventually can escape from the specimen 201,as shown in FIG. 40A.

In addition, upon departure from the specimen 201, a relatively largeamount of reflection electrons generate secondary electrons 203a. Thegeneration amount of the secondary electrons 203a depends on the amountand energy of the irradiated electron beam 202a. Since the electron beam202a now reflected has information about the hole bottom 208 andinternal structure 209, that is, test parts, images of the hole bottom208 and internal structure 209 can be obtained by detecting an imagesignal indicative of the secondary electrons 203a.

More particularly, by detecting secondary electrons 203 and secondaryelectrons 203a generated by reflection electrons scattered in the insideof the specimen 201 in combination, a hole bottom part, a side wall partof a bank, a buried internal part or a conical hole part which is shadedfrom the electron beam 202a can be displayed in combination with such aspecimen image as shown in FIGS. 41B, 42B, 43B or 44B which can beobserved with the prior art, thereby permitting a display including apart unseen in the direction of irradiation of the electron beam 202awhich is hatched in FIGS. 41C, 42C, 43C or 44C.

Referring now to FIGS. 45A, 45B, 46A, 46B, 47A and 47B, photographicexamples of specimen images taken by the technique of the presentinvention will be described by making a comparison with conventionalphotographic examples taken with the scanning electron microscope.

In this case, the monochromatic (white/black) density is determined inaccordance with generation amounts of secondary electrons 203 and 203a,and the larger the generation amounts of secondary electrons 203 and203a, the lighter the photographed color becomes. Conversely, thesmaller the generation amounts, the darker the photographed colorbecomes.

In obtaining the photographs shown in FIGS. 45A and 45B in connectionwith the specimen 201a having hole structure 204 corresponding to thestructure of FIG. 41A, a hole in a resist of a resist pattern formed ona semiconductor wafer, for example, is observed with the scanningelectron microscope.

In this case, with the prior art, an edge of the hole and a side wallportion which can be seen in the direction of irradiation of theelectron beam are photographed in light color and the hole bottom and aresist portion surrounding the hole are photographed in dark color, asshown in FIG. 45A. The hole bottom part shaded by the hole wall from theelectron beam cannot be displayed in a specimen image in this manner butaccording to the present embodiment, a specimen image combined with theconcealed hole bottom part displayed in light color can be photographedas shown in FIG. 45B.

In connection with a specimen 201b having a bank structure 205 as shownin FIG. 42A, a semiconductor wafer formed with a resist pattern isobserved as in the case of the photographs of FIGS. 45A and 45B toobtain a photograph as shown in FIG. 46B which demonstrates that a sidewall of resist at a position opposite to an electron beam and shadedtherefrom can be photographed and observed in lighter color as comparedto a photograph of FIG. 46A taken with the prior art. Further, in thephotograph of FIG. 46B, a depressed portion of a contact hole standingfor an inner structure can be photographed in darker color than thesurface resist portion.

A wiring pattern having, for example, two-layer wiring structure isphotographed to obtain photographs as shown in FIGS. 47A and 47B. In thephotograph of FIG. 47A taken with the prior art, only a side wall ofsurface wiring is photographed in light color but an internal structurecannot be photographed in dark and light color and the presence of aninternal structure cannot even be inferred. In the present embodiment,however, as shown in FIG. 47B, even the undersurface wiring buriedinternally can be photographed in lighter color than its surroundingsand can be observed in combination with the surface upper-layer wiring.

Observation conditions for the photograph shown in FIG. 47A are asfollows: acceleration voltage: 3 keV; emission current: 10 μA;magnification in observation (magnification on photograph):×15K (×6.35);inclination of specimen: 0°; and working distance: 5 mm (minimum).Thereby, the shape of a PRO layer is only observed. The shape observedshows ups and downs reflecting a wiring M2 (see FIG. 47C).

Observation conditions for the photograph shown in FIG. 47B are asfollows: acceleration volt age: 200 keV; emission current: 10 μA;magnification in observation (magnification on photograph):×15K (×7.5);inclination of specimen: 0°; and working distance: 8 mm (minimum).Thereby, the shape of a PRO layer is observed. The shape observed showsups and downs reflecting the wiring M2. Furthermore, FIG. 47C showsshapes of the wiring M2, a wiring M2 in a middle layer, and holes ofCONT that are observed. It is difficult to observe the shape of a holeright under the wiring M2.

Thus, in accordance with the image display method of the presentembodiment, by using as they are a signal indicative of ordinarysecondary electrons 203 and a signal indicative of secondary electrons203a due to reflection electrons scattered in the inside of a specimen201 under the application of an electron beam 202a at a very high speed,a specimen image of a specimen part which is unseen in the direction ofirradiation of the electron beam 202a can be displayed while beingsuperimposed on a specimen image of a specimen part which is seen in thedirection of irradiation of the electron beam 202a and so can bedisplayed with the prior art, thereby making it possible to observe adisplay including the part which cannot be seen with the conventionalmethod.

The image observing method of the present embodiment has been describedas being exemplified such that a signal indicative of secondaryelectrons 203a due to reflection electrons scattered in the inside of aspecimen 201 is used, as it is, as an information source for displayinga part which is unseen in the direction of irradiation of an electronbeam 202a, but the present invention is in no way limited to theforegoing embodiment and may also be applied widely to other methods asdescribed below.

More particularly, in the case where an image signal indicative ofreflection electrons or X-rays generated from a specimen under theapplication of an electron beam is utilized as an information source fordisplaying an unseen part as in the foregoing embodiment, a method maybe employed wherein the signal indicative of reflection electrons orX-rays is processed and then used for image display.

In this case, in addition to, for example, a specimen image due toordinary secondary electrons, an image due to X-rays may be fetched, thetwo images are compared with each other to calculate information about aconcealed part such as an internal structure, and the thus calculatedinformation may be displayed while being superimposed on the image dueto ordinary secondary electrons. Further, secondary electrons resultingfrom interaction of X-rays or secondary electrons generated from a testpart such as hole bottom 208 or internal structure 209 with the surfaceof a specimen may be used to form an image, and this image may besuperimposed on a surface image of the specimen.

Further, a method may be employed wherein design information such aspattern/structure data of LSI is used as an image signal. For example,as shown in FIG. 48, pattern data concerning a specimen and devicestructure information are previously stored in a data base (memory 210),information about the observing direction/position, inclination and areaof an image observing field is detected by controller 214 whenperforming observation with a scanning electron microscope 215, and thedata are read out of the data base 210 and subjected to computer graphicprocessing by means of an image generator 212. A graphic image thusobtained is superimposed on an image produced from the scanning electronmicroscope 215 by means of a composer 213 and displayed on a display216. In this case, the irradiation energy of an electron beam in thescanning electron microscope 215 is determined for exclusive use inobservation of the specimen surface and is of 0.5 to 20 KeV.

Furthermore, when performing display of the specimen image as above,display of the concealed part may be characterized by, for example,color display or contour display.

While in the foregoing description, the present invention has beendescribed as being applied mainly to the scanning electron microscopeused for fabricating semiconductor wafers, it is not limited thereto andmay also be applied widely to related apparatus or similar apparatususing a scanning electron microscope and to all of the fields utilizingthese apparatus; especially, the invention may be applied preferably tothe case where observation of a specimen inclusive of a part thereofwhich is unseen in the direction of irradiation of an electron beam isneeded.

Briefly, effects brought about by the present embodiment are as follows.

More particularly, by providing a superimposed display of a specimenimage of a specimen part which is seen in the direction of irradiationof an electron beam and a specimen image of a specimen part which isunseen in the direction of irradiation of the electron beam, a partwhich cannot be observed using only an ordinary secondary electron imagecan be displayed, and therefore a greater amount of information,including, for example, three-dimensional shapes and three-dimensionalsizes, can be obtained.

Consequently, a display method for a specimen image in a scanningelectron microscope can be provided which can visualize a partconventionally unseen by the scanning electron microscope and can widenand depend knowledge obtained from a specimen image.

FIG. 49 shows, in block form, a scanning electron microscope accordingto another embodiment of the present invention. The scanning electronmicroscope has all components of the conventional scanning electronmicroscope, but only components necessary for explaining the presentinvention are depicted in the figure.

An electron beam 301 of high energy emitted from an electron source(illustration of the electron source as well as the acceleratingelectrode, condenser lens and the like is omitted) is deflected by anupper scanning coil 302 and a lower scanning coil 303 which arecontrolled by a scanning controller 315, so as to be faster-scanned on aspecimen 305 after having passed through the lens center of an objectivelens 304. A CPU 320 suitably sets and output of the scanning controller315 on the basis of a magnification inputted in advance from a keyboard319 to determine a range for the electron beam 301 to be scanned on thespecimen 305.

The specimen 305 is carried on a specimen stage 310 comprised of an Xinclining stage 307, a Y inclining stage 308 and an XY moving stage 309,and the specimen stage 310 is controlled by a stage controller 311 so asto be driven in respective directions. Secondary electrons 312 generatedfrom the surface of the specimen 305 during scanning of the electronbeam 301 are detected by a secondary electron detector 313 and amplifiedby a video amplifier 314. A thus-amplified secondary electron signal isinputted to a scanning image display unit 316 as a brightness modulationsignal for the scanning image display unit 316 which is scanned insynchronism with the electron beam 301 to provide a scanning imagedisplayed on the screen.

The secondary electron signal amplified by the video amplifier 314 is,on the other hand converted by an A/D converter 317 into digital datawhich in turn is stored in an image memory 318. When the CPU 320 readsimage data from the image memory 318, it recognizes a position of anobject subject to length measurement by utilizing known patternrecognition techniques and performs an article dimension measurementoperation on the basis of a result of detection of an edge at thatposition and the aforementioned enlargement magnification. In otherwords, a distance between detected edges is measured.

The specimen stage 310 described hereinbefore preferably does notinclude any rotation mechanism but in the case where a rotationmechanism is included, a rotation angle may be reflected on athree-dimensional model. In such a rotation mechanism, at least one ofthe specimen stage and the scanning direction is rotated in relation tothe other. For example, as hardware for generating an electron beam ofhigh energy, a TEM (type: HF-2000) offered by Hitachi, Ltd., can beutilized, and as the other hardware and software for image formation andlength measurement, an article Dimension Measurement SEM (type: S-6280)offered by Hitachi, Ltd., can be utilized.

In the present embodiment, by using an electron beam of high energy, aportion which cannot be observed with the low acceleration SEM can beobserved, thereby ensuring that the length of an object whose length hasnot been measured in the past or that of an object whose length couldnot be measured without suffering from a large measurement error can bemeasured with high accuracy. Preferably, the accelerating voltage forthe electron beam is set to 50 keV or more, and more preferably, to 100to 200 keV. In place of the electron beam, another charged particle beamsuch as an ion beam can be used.

Referring now to FIG. 50, an observing method employing a high-energyelectron beam will be described. As will be seen from the figure, in acontact hole formed in the surface of a substrate and having an invertedtaper form, the entirety of contour of the bottom of the contact holecannot be observed at a time even when the specimen is inclined invarious ways. More particularly, even when the diameter of the bottom isdesired to be measured, one of the article dimension measuring start andend points is always blocked visually by another portion of the specimenas viewed in a direction of irradiation of the electron beam, so thatthe start and end points cannot be viewed simultaneously, thus making itimpossible to perform the article dimension measurement.

However, when an electron beam 343 of high energy is irradiated,secondary electrons 346 are generated from the surface of a substrate345, secondary electrons 347 are generated from the side wall of acontact hole, and secondary electrons 348 are generated from the bottomsurface of the contact hole by the electron beam 343 which hastransmitted through a portion of the substrate and irradiated the bottomsurface. Further, reflection electrons 349 generated from the bottomsurface impinge on the side wall to generate secondary electrons 347 andleave the surface while generating secondary electrons 341 from thesurface. On the other hand, when an electron beam irradiates a surfaceportion which is clear of the taper portion, only secondary electrons346 are generated from the surface portion. With an electron beam 343irradiated directly on the bottom surface, reflection electronsgenerated from the bottom, surface produce signals indicative ofsecondary electrons 347 generated from the side wall and secondaryelectrons 341 generated from the surface.

Comparison of signals generated from the substrate surface, the holebottom surface, and the taper portion of the hole side surface, showsthat a signal generated from the taper portion is of the highestintensity and, therefore, when the contact hole in the form of aninverted taper is observed using an electron beam of high energy, thetaper portion is observed as a light ring 342 as shown in FIG. 51.Accordingly, direct measurement of a diameter A of the top surface and adiameter B of the bottom surface can be ensured.

When the present embodiment is applied, a scanning image as shown inFIG. 52 can be observed, demonstrating that the contour of the bottom,which could not be observed with the low acceleration SEM, can beobserved.

Referring to FIG. 54, when an electron beam 343 of high energy isirradiated on a specimen having in exposed wiring line 374 provided onthe surface of a substrate and a wiring line 375 embedded in thesubstrate, the electron beam 343 reaches the embedded wiring line 375 togenerate reflection electrons 359 thereat, and the reflection electronsgenerate secondary electrons 351 from the surface. Accordingly, bydetecting the secondary electrons 351 generated from the surface, theembedded wiring line 375 can be observed. In addition, since the wiringline 374 on the surface can be observed with ease, measurement of adistance P between the wiring line 374 on the surface and the embeddedwiring line 375, which has hitherto been impossible to achieve, can bepermitted. See FIG. 55.

When an isolated line of a resist pattern has a side surface of aninverted taper form and is irradiated with a high-energy beam, ascanning image and a line profile signal as a result of measurement ofsignal intensity carried out along the isolated line are obtained asshown in FIG. 53. Illustrated in FIG. 56 is a typical example of theline profile signal obtained by measuring the signal intensity acrossthe isolated line of a resist pattern having a side surface of aninverted taper form. In this case, amounts of secondary electronsgenerated from the top surface, S1, and of secondary electrons generatedfrom the side surface, S2, differ from each other and, therefore, if thecross-sectional shape of the wiring pattern is known to be eithertrapezoidal as shown in FIG. 57A or inverted trapezoidal as shown inFIG. 57B, geometrical dimensions of individual portions can becalculated.

In experiments conducted by the inventors of the present invention, therelation between a taper angle θ and a signal ratio (S2/S1 in FIG. 56)in the case of the non-inverted taper side surface, is compared withthat in the case of the inverted taper side surface to indicate that thesignal ratio is larger in the latter case than in the former case asshown in FIG. 58. Hence, by simply making reference to the line profileas shown in FIG. 56, a cross-sectional shape of the wiring pattern canalso be recognized.

Referring now to FIG. 59A, there is seen an example of a scanning imageobtained when a pattern of a rectangular parallelepiped having arectangular cross-section is inclined (see FIG. 59B) and observed. Withan electron beam of high energy is irradiated, amounts of secondaryelectrons generated from the top, bottom and side surfaces are differentfrom each other, and the boundary line between adjacent surfaces cantherefore be recognized. Accordingly, the height of a wiring pattern canbe calculated from widths of both side surfaces and an inclination angleof the specimen stage.

A line profile signal obtained in this case indicates that a secondarysignal generated from the right side surface in the picture is largerthan that generated from the left side surface and, as will be seen fromthe experimental results shown in FIG. 58, it can also be recognizedthat the right side surface corresponds to an inverted taper portion andthe left side surface corresponds to a non-inverted taper portion.

According to the present embodiment, an electron beam reaches a depth ina specimen, and a scanning image of a portion which is exposed to thespecimen surface but is visually blocked by another portion when viewedin direction of irradiation of the electron beam, or a scanning image ofa portion which underlies another portion so as to be prevented frombeing exposed to the specimen surface, can be observed simultaneouslyand similarly to a scanning image of a portion that is exposed to thespecimen surface. Therefore, article dimension measurement can beensured in connection with such a portion.

FIG. 60 shows, in block form, the construction of a scanning electronmicroscope according to still another embodiment of the presentinvention. In the figure, components identical or equivalent to those ofFIG. 49 are designated by identical reference numerals. The presentembodiment features the additional provision of a three-dimensionalmodel generator 330 for generation of a graphic three-dimensional modelwhich is displayed by being superimposed on through-holes and wiringpatterns displayed on the scanning image display unit 316. The presentembodiment does not always require the electron beam to be a high-energybeam, but may also be applied to the conventional low acceleration SEM.

FIG. 61 is a functional block diagram showing the construction of thethree-dimensional model generator 330. In the figure, the samecomponents as those described previously are designated by likereference numerals.

Referring to FIG. 61, a three-dimensional model storage 401 stores shapedata concerning a variety of three-dimensional models such as columns,prisms and rectangular parallelepipeds. A three-dimensional modelselector 402 selectively reads shape data of a three-dimensional model,conforming to a command from an operator, from the three-dimensionalmodel storage 401. A three-dimensional model former 403 forms athree-dimensional model on the basis of the shape data selected by thethree-dimensional model selector 402. The thus-formed three-dimensionalmodel undergoes various kinds of control by posture controller 404 andposition controller 405 to be described later, and thereafter it isdisplayed on the scanning image display unit 316.

A shape changer 407 changes shape data of the three-dimensional model onthe basis of a command from the operator to change the shape of thethree-dimensional model being displayed. The posture controller 404decides conditions of the specimen stage 310 (such as an inclinationangle of the X inclining stage 307 and an inclination angle of the Yinclining stage 308) from a state controlled by the stage controller311, and controls the posture of the three-dimensional model such thatrelative matching of the posture of the three-dimensional modeldelivered out of the three-dimensional model former 403 to the postureof a scanning image can be attained. The position controller 405translates, on the screen, a display position of the three-dimensionalmodel at which the relative posture matching to the scanning image isobtained. An article dimension calculator 406 calculates articledimensions of individual portions of the three-dimensional model on thebasis of the shape of the three-dimensional model and an enlargementmagnification.

Operation of the present embodiment will now be described in greaterdetail by considering observation and article dimension measurement ofan actual pattern, for instance.

Depicted in FIG. 62 is a scanning image 500 obtained by observing acontact hole of an inverted taper form while inclining the specimenstage 310. As shown, only part of contour 501, side surface 504 andbottom surface 503 of an opening and only part of contour 502 of thebottom surface 503 can be observed.

The operator manipulates the keyboard 319 to designate a column as athree-dimensional model of an object to be observed which is predictedfrom the scanning image, and inputs dimensions of some portions of theobject if the dimensions are known. A description will be givenhereinafter on the assumption that a diameter of the opening isinputted. The three-dimensional model selector 402 selectively readsshape data of the column from the three-dimensional model storage 401.The three-dimensional model former 403 forms a wire model(three-dimensional model) 600 of the column as shown in FIG. 63 on thebasis of the read shape data, an enlargement magnification and theaforementioned known geometrical dimension.

In order to attain the relative posture matching of the scanning image500 to the three-dimensional model 600 on the screen, the posturecontroller 404 determines an inclined state of the specimen stage 310 onthe basis of data from the stage controller 311 and controls the postureof the three-dimensional model 500 on the screen. FIG. 64 shows anexample of display of the scanning image 500 and three-dimensional model600 on the screen obtained after completion of posture control,indicating that the inclined state of the scanning image 500 matches theinclined state of the three-dimensional model 600.

Subsequently, the operator manipulates the keyboard 319 to move thethree-dimensional model 600 so that contour 501 of the opening of thescanning image 500 may be coincidentally superimposed on contour 601 ofthe top surface of the three-dimensional model 600. In the presentembodiment, complete matching of the contour of the opening to that ofthe top surface can be accomplished because the diameter of the openinghas been previously inputted as the known dimension, but contour 502 ofthe bottom surface of the scanning image 500 does not match contour 602of the bottom surface of the three-dimensional model 600 because thecontact hole has an inverted taper form and the contour 502 of thebottom surface is larger than the contour 501 of the opening.

Accordingly, the operator manipulates the keyboard 319 to enlarge thediameter of bottom surface of the three-dimensional model and expand orcontract the height of the three-dimensional model in order that part ofthe contour 502 of the contact hole bottom surface matches the contour602 of the three-dimensional model bottom surface, as shown in FIG. 66.

When the complete matching of the contour of the scanning image 500 tothe contour of the three-dimensional model 600 is accomplished, thethree-dimensional model 600 has the same shape as the contact hole andtherefore, the geometrical dimension calculator 406 calculatesgeometrical dimensions of unknown portions on the basis of the shape ofthe three-dimensional model 600 and an enlargement magnification, anddelivers results of calculation for display thereof.

FIG. 67 diagrammatically shows a method of calculating geometricaldimensions of unknown portions When only the diameter of the opening isknown as in the case of the present embodiment, geometrical dimensionsof lengths of other portions can be calculated as will be describedbelow.

More specifically, the diameter of the bottom surface can be determinedby directly measuring the diameter of the bottom surface of thethree-dimensional model. When lengths of portions c, d and e aremeasured with the three-dimensional model inclined as shown in thefigure, a geometrical dimension f can be calculated from equation (1) asfollows.

    f=e-(c/2)-(d/2)                                            (1)

As shown in FIG. 68, when the inclination angle of the specimen is θ, adepth D of the contact hole can be calculated from equation (2) asfollows:

    depth D=f/sinθ                                       (2)

The foregoing embodiment has been described wherein the known diameterof the contact hole opening is inputted initially and thethree-dimensional model sized to conform to the input value is displayedinitially but a three-dimensional model may be displayed by designatingonly a shape and then may be modified in size, including sizemodification of the top surface, so as to match a scanning image. Theobject to which the length-measuring method described so far is appliedis not limited to the three-dimensional model, but may also be ascanning image obtained in the foregoing embodiment.

According to the present embodiment, even when only part of a contour ofan object is allowed to be observed, the whole contour can be predictedby utilizing a three-dimensional model and the shape of the object to beobserved can be represented by the shape of the three-dimensional mode.Therefore, by measuring geometrical dimensions of the three-dimensionalmodel, lengths of portions not exposing to the specimen surface can bemeasured.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade thereto without departing from the spirit and scope of the presentinvention as defined by the appended claims.

We claim:
 1. An apparatus for displaying a scanning electron image onthe basis of electrons emitted from a specimen, comprising:means fordisplaying a model representing a bottom of a contact hole on an imageof said specimen; means for changing at least one of a position and ashape of said model on said specimen, to produce a changed model; andmeasuring means for measuring a dimension of said changed model.
 2. Anapparatus for displaying a scanning electron image according to claim 1,wherein the dimension measured by said measuring means is a diameter ofsaid changed model.
 3. An apparatus for displaying a scanning electronimage on the basis of electrons emitted from a specimen,comprising:means for displaying a model representing at least a portionof a pattern on an image of said specimen; means for changing at leastone of a position and a shape of said model on said specimen, to producea changed model; and means for measuring a dimension of said changedmodel.
 4. An apparatus for displaying a scanning electron image on thebasis of electrons emitted from a specimen, comprising:means fordisplaying a model representing a bottom of a contact hole on an imageof said specimen; changing means for changing at least one of a positionand a radius of said model on said specimen; and means for measuring adimension of said model changed by said changing means.